IC class T0-T2 taps with and without topology selection logic

ABSTRACT

Topology discovery of a target system having a plurality of components coupled with a scan topology may be performed by driving a low logic value on the data input signal and a data output signal of the scan topology. An input data value and an output data value for each of the plurality of components is sampled and recorded. A low logic value is then scanned through the scan path and recorded at each component. The scan topology may be determined based on the recorded data values and the recorded scan values.

CLAIM OF PRIORITY

This Application is a divisional of prior application Ser. No.14/101,871, filed Dec. 10, 2013, now U.S. Pat. No. 8,826,088, grantedSep. 2, 2014;

Which is a divisional of prior application Ser. No. 13/948,373, filedJul. 23, 2013, now U.S. Pat. No. 8,631,289, granted Jan. 14, 2014;

Which is a divisional of prior application Ser. No. 13/560,470, filedJul. 27, 2012, now U.S. Pat. No. 8,522,093, granted Aug. 27, 2013;

Which is a divisional of prior application Ser. No. 12/511,957, filedJul. 29, 2009, now U.S. Pat. No. 8,255,749, granted Aug. 28, 2012.

The present application claims priority to and incorporates by referenceU.S. Provisional Application No. 61/084,474 filed Jul. 29, 2008,entitled “Topology Discovery Training ”

The present application also claims priority to and incorporates byreference U.S. Provisional Application No. 61/084,471 filed Jul. 29,2008, entitled “Series Equivalent Scans Across Multiple ScanTopologies.”

The present application also claims priority to and incorporates byreference U.S. Provisional Application No. 61/084,463 filed Jul. 29,2008, entitled “Selecting a Scan Topology.”

The present application also claims priority to and incorporates byreference U.S. Provisional Application No. 61/084,458 filed Jul. 29,2008, entitled “Automatic Scan Format Selection Based on Scan TopologySelection.”

The present application also claims priority to and incorporates byreference U.S. Provisional Application No. 61/084,453 filed Jul. 29,2008, entitled “Dynamic Broadcast of Configuration Loads SupportingMultiple Transfer Formats.”

The present application also claims priority to and incorporates byreference U.S. Provisional Application No. 61/084,439 filed Jul. 29,2008, entitled “Timing Protected Detection of Alternate SignalingMechanism Using Clock and Data.”

FIELD OF THE INVENTION

This invention generally relates to the field of testing integratedcircuits and systems containing integrated circuits.

BACKGROUND OF THE INVENTION

The IEEE 1149.1 standard was adopted in 1990. Built upon the work of theJoint Test Action Group (JTAG), it provided a pins-out view from one ICpad to another to help test engineers locate and discover faulty PCboards. A description of the boundary scan description language wasadded in 1994.

Complications arose as chips increased functionality and designs shiftedaway from PC boards to multichip modules and stacked die packages. Thesedifficulties included handling the pin count requirements and multipleTest Access Port (TAP) controllers for System-on-Chip (SoC) devices,testing multichip modules and stacked die configurations, enhancingdebug performance, and improving test and debug logic power-down inlow-power conditions.

Organizations like the Mobile Industry Processor Interface Alliance andthe NEXUS 5001 Forum took up the challenge to solve the problemsspecific to their industries.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments in accordance with the invention will now bedescribed, by way of example only, and with reference to theaccompanying drawings:

FIG. 1 is a block diagram illustrating a target system with series scantopology;

FIG. 2 is a block diagram illustrating a target system with four-wirestar scan topology;

FIG. 3 is a block diagram illustrating a target system with two-wirestar scan topology;

FIG. 4 is a block diagram of a target system with mixed use oftechnologies and scan topologies;

FIG. 5 is an illustration contrasting 1149.1 and 1149.7 test views;

FIG. 6 is a series topology with mix of TAP.7s plus TAP.1s or TAP.7swith no TSL;

FIG. 7 is a block diagram illustrating TAP.7 TAPC hierarchy;

FIG. 8 is an illustrative block diagram of system connectivity supportedby TAP.7 architecture;

FIG. 9 is a block diagram illustrating system connectivity supported bythe TAP.7 architecture;

FIG. 10 is a block diagram illustrating bypass bits; and

FIG. 11 is a flow diagram illustrating topology discovery in a targetsystem.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

As chips add new functionality and system designs evolve away fromboards and toward multi-chip system-on-chip (SoC) architectures,developers of handheld and consumer electronics are faced with stricterpin and package constraints. The IEEE 1149.7 standard is a new two-pintest and debug interface standard that supports half the number of pinsof the IEEE 1149.1 technology, allowing developers to easily test anddebug products with complex digital circuitry, multiple CPUs andapplications software in products such as mobile and handheldcommunication devices.

Systems and integrated circuits that utilize IEEE 1149.7 may be designedto include a complex scan topology. Circuits and methods for determiningthe scan topology during a test session will be described in more detailbelow.

The IEEE 1149.7 is a complementary superset of the widely adopted IEEE1149.1 (JTAG) standard that has been in use for more than two decades.This standard defines a port into embedded systems for devicemanufacturing, testing and software development during systemdevelopment. In addition to maintaining compatibility with IEEE 1149.1,the new standard improves debug capabilities and reduces SoC pin-countrequirements. It also standardizes power-saving conditions, simplifiesmanufacturing of multi-chip modules and stacked die devices, andprovides the ability to transport instrumentation data. Concepts andterminology used in IEEE 1149.1 and in IEEE 1149.7 are used in a similarmanner herein and are therefore not described in detail herein.

Rather than replacing IEEE 1149.1, the new IEEE 1149.7 standard expandsits functionality while reducing the number of pins used in someconfigurations. It supports new scan topologies that are favorable tostacked die and multichip module configurations and offers advancedcapabilities to aid in software debug. It describes circuitry that maybe added to an integrated circuit to provide access to on-chip IEEEstandard test access ports (TAPs) specified by IEEE Std 1149.1- 2001. Itprovides complete backward compatibility with the 1149.1 standard whileaggressively adding features to supporting applications test and debug.The circuitry uses IEEE Standard 1149.1-2001 as its foundation.

The 1149.7 Standard delivers these capabilities with six classes of testaccess ports (T0-T5), with each class providing incremental capability.The IEEE 1149.7 standard has two groups of capabilities: Classes T0through T3, which extend IEEE 1149.1 and enable new operations using theIEEE 1149.1 protocol, and Classes T4 and T5, which are focused onadvanced two-pin operation using an Advanced Protocol.

Class T0 ensures compliance with the industry's test infrastructure bysetting up IEEE 1149.7 devices to make them act compatibly with IEEE1149.1. These techniques include the use of N-bit IR, 1-bit DR forbypass instruction, mandatory IDCODE (32-bit path), and mandatoryinstructions behaving as specified in the IEEE 1149.1 specification.After a test logic reset is initiated, all multi-TAP devices mustconform to the mandatory IEEE 1149.1 instruction behavior and implementa 1-bit DR scan for the bypass instruction. FIG. 1 illustrates such asystem. Debug test system (DTS) 100 is generally a computer based systemthat provides control and a user interface for testing an integratedchip, printed circuit board or SoC using IEEE 1149.1 that has beenenhanced to support the IEEE 1149.7 protocols. DTS 100 may be an XDSemulator from Texas Instruments, for example. Modules 110(1)-110(n) arerepresentative of various modules that may be interconnected to DTS 100using various aspects that will be described in more detail below.

Class T1 instantiates a control system for the IEEE 1149.7 standard thatis transparent to IEEE 1149.1 devices, providing a foundation for theadvanced functionality implemented in Classes T1 through T5 withoutchanging the IEEE 1149.1 state machine. It supports standardized testand functional resets along with power management of the TAP controllerand test logic.

Class T2 offers a chip-level bypass mechanism that shortens scan pathsand another mechanism that provides hot connect capability to achievehigher performance for testing high chip count applications,

Class T3 provides for boundary scan testing using a four signal startopology (Star-4), with TAP selection built into the TAP.7 controller,unlike the use of a Star-4 Scan Topology described by the IEEE 1149.1Standard. A T3 TAP may be deployed in either a series or star scantopology. A star topology is preferable for testing stacked dieconfigurations. Whereas FIG. 1 shows the series scan topology, FIG. 2illustrates the Star-4 or Wide Star configuration. In this case, modules210(1)-210(n) are connected in a parallel manner using four wires andmay be connected to DTS 200 that is configured to provide control over astar connected system, as will be described in more detail below. Directaddressability is included with T3 and above TAP.7 controllers.

Class T4 provides a reduction of number of test and debug pins in SoCdevices. It supports scan transactions with two pins instead of four,resulting in fewer total pins required on chip packages. This also helpswith stacked die configurations because it is highly desirable to havedebug pins connected in parallel when dies are stacked. Two-pinoperation is provided by eliminating the original data lines and sendingbidirectional serialized data over the Test Mode Select (TMS) line,which is renamed TMS Counter (TMSC). To implement this capability, theglueless star configuration from Class T3 is utilized, this time withoutTest Data In (TDI) and Test Data Out (TDO). This is the Star-2configuration shown in FIG. 3 in which an illustrative SoC 300 includesseveral die 302(1)-302(n) connected in a Star-2 arrangement using onlytwo wires in a parallel manner. Of course, other embodiments may havefewer or more die and still use the two pin interconnection. Otherembodiments may use the two pin interconnect for interconnection ofpackaged chips as well as bare or stacked die.

To address the rising number of pins in SoC devices, Class T4 adds scanformats to support transactions with two pins instead of four, resultingin fewer total pins required on chip packages. This also helps withstacked die configurations because it is highly desirable to have thefewest number of connectors possible when die are stacked. The key totwo-pin operation is eliminating the original data lines and sendingbidirectional serialized data over the Test Mode Select (TMS) line,which is renamed TMS Counter (TMSC). To implement this capability, theglueless star configuration from Class T3 is utilized, this time withoutTest Data In (TDI) and Test Data Out (TDO). This is the Star-2configuration shown in FIG. 3 in which an illustrative SoC 300 includesseveral die 302(1)-302(n) connected in a Star-2 arrangement using onlytwo wires in a parallel manner. Of course, other embodiments may havefewer or more die and still use the two pin interconnection. Otherembodiments may use the two pin interconnect for interconnection ofpackaged chips as well as bare or stacked die.

Besides reducing pin count, Class T4 defines optimized download-specificscan modes in which only useful information is downloaded. To improvepin operation performance, the clock rate also can be doubled. Thesefeatures combined with the optimized transactions do not causeperformance loss, instead improving performance in some cases.

Class T5 functionality is beneficial primarily to software designersutilizing a Test Access Port for debugging. This class gives the testport the ability to perform debug and instrumentation operationsconcurrently (data is transferred during idle time), which reduces thenumber of pins dedicated to instrumentation, and enables customprotocols to use the pins, a feature many vendors offer in nonstandardways. Class T5 standardizes the process used to access the pins andprovides both scan and data transport transactions using the two wireinterface.

FIG. 3 also illustrates a debug test system (DTS) 310 coupled to SoC300. DTS 310 is generally a computer based system that provides controland a user interface for testing an integrated chip, printed circuitboard or SoC using IEEE 1147.1 that has been enhanced to support theIEEE 1147 protocols and two-wire interface, as will be described in moredetail below. DTS 310 may be an XDS emulator from Texas Instruments, forexample.

T0-T3, and T4/T5 four pin TAP.7s may be deployed in a Series Scantopology. T3 and T4/T5 four pin TAP.7s may be deployed in a Star-4 Scantopology. T4-T5 TAP.7s may be deployed in a Star-2 Scan Topology. Whendeployed in these scan topologies, all classes can traverse the statediagram using a common protocol (Standard- the legacy IEEE 1149.1protocol). In the Series Scan Topologies data transfers to conventional1149.1 instruction and data registers are performed with the StandardProtocol. In the Star-4 scan topology data transfers are performed withthe Standard Protocol modified to prevent drive conflicts, with theability to select the scan paths of only one TAP.7 controller in thetopology at a time. This provides for sequential access to the paths ofeach TAP.7 controller in the branch. In the Star-2 scan topology, datatransfers are performed only with the Advanced Protocol. The selectionmechanisms for scan paths and TAPCs available with Star-4 operation arealso available with Star-2 operation. Classes T0-T2 allow the use onlythe Standard Protocol, Class T3 allows the use of the Standard Protocolto traverse the TAPC state diagram and a modified Standard Protocol toeither traverse the state diagram or perform data transfers in theShift-IR and Shift-DR states. Classes T4 and T5 allow the use of theStandard Protocol to traverse the TAPC state diagram, a modifiedStandard Protocol to either traverse the state diagram or perform datatransfers in the Shift-IR and Shift-DR states, when operated in a Star-4Scan Topology, and Advanced Protocols to either traverse the statediagram or perform data transfers in the Shift-IR and Shift-DR stateswhen operated in a Star-2 Scan Topology. It is important to note thatwith deployment in Star-4 and Star-2 topologies, TAP.7 controllersperform data transfers in these scan topologies using protocols uniqueto the topology in which they are deployed.

With Series Equivalent Scans, the selection of a single branch initiatesthe use of the protocol required to transfer data, while the selectionof all branches initiates the use of the Standard Protocol since onlytraversing the state diagram is needed.

The operation of each of these Scan Topology Branches supports theselection of individual TAPCs and the scan paths associated with themduring their independent operation. This is covered in the 1149.7standard and not in this description.

TAP.7 architecture provides for the operation of Series, Star-4, andStar-2, Scan Topologies and other technologies sharing the TCK(C),TMS(C), TDI(C), and TDO(C) connections to a Debug Test System directingscan activity. These Scan Topologies are called branches of the systemscan topology. With this architecture, an Adapter Test Access PortController (ADTAPC) is the gateway to scan facilities of a chipimplementing an 1149.7 Test Access Port. The ADTAPC controls access to aChip-Level Test Access Port Controller (CLTAPC) that provides access tochip-level scan paths

Since a typical boundary scan operation requires scanning theinstruction registers and boundary scan cells of one or more devicesbetween the Select-xR and Update-xR states, a method is needed toduplicate the scan transaction available with a Series Scan topologywhen more than one scan topology is involved. With this description,states such as the Capture-xR and Update-xR TAP are to be interpreted asfollows: the “x” refers to either “D” for data or “I” for instruction.Embodiments of the invention provide this equivalent function, a seriesequivalent scan.

Series equivalent scans of a complex scan topology, i.e., a scantopology with two or more branches in which at least two of the branchesare of differing technologies (see Table 1), sharing the same controland data signaling create the equivalent of an 1149.1 series scan thatbegins with the Select-xR state and ends with the Update-xR state. Witha series Scan Topology, all scan paths of interest are scanned at thesame time between these states. With a complex scan topology, this isnot possible as methods used to transfer data to and from scan pathspresented by Series, Star-2, and Star-4 Scan Topologies and othertechnologies is different.

With series equivalent scans, a scan is broken into sections consistingof one or more scan sections. With an 1149.7 Test Access Port, the scansection is one or more sequences of the Exit2-xR, one or more Shift-xRstates, Exit1-xR, and one or more Pause-xR states. With anothertechnology, scan data would be delivered as defined by the technology.These scan sections are sandwiched between a preamble (Select-xR,Capture-xR, Exit1-xR, and one or more Pause-DR states) and a postamble(Exit2-xR and Update-DR states). A single branch is selected between thepreamble and the first scan section and between scan sections. Allbranches are selected between the last scan section and the postamble.With the sequence described above, all or some CLTAPCs in all branchesprogress from either the Test-Logic-Reset or Pause-xR state to thePause-xR state without encountering an Shift-xR state. The TAPCs of allbranches of interest operate in lockstep during the preamble andpostamble state sequences, with only the TAPCs within branches that areselected during scan sections.

TABLE 1 Protocol usage by Technology TAPC Topology Operation of BranchesState Protocol Selected Series Star-4 Star-2 Other Select-xR StandardAll Active Active Active Active Capture-xR Standard All Active ActiveActive Active Exit1-xR Standard All Active Active Active Active Pause-xRStandard All Active Active Active Active — — — Select-Series. Pause-xRStandard Series Active Dormant Dormant Dormant Exit2-xR Standard SeriesActive Dormant Dormant Dormant Shift-xR Standard Series Active DormantDormant Dormant — — — Shift-xR Standard Series Active Dormant DormantDormant Exit1-xR Standard Series Active Dormant Dormant Dormant Pause-xRStandard Series Active Dormant Dormant Dormant — — — Select-Star-2Pause-xR Advanced Star-2 Dormant Dormant Active Dormant Exit2-xRAdvanced Star-2 Dormant Dormant Active Dormant Shift-xR Advanced Star-2Dormant Dormant Active Dormant — Shift-xR Advanced Star-2 DormantDormant Active Dormant Exit1-xR Advanced Star-2 Dormant Dormant ActiveDormant Pause-xR Advanced Star-2 Dormant Dormant Active Dormant — — —Select-Star-4 Pause-xR Modified Std Star-4 Dormant Active DormantDormant Exit2-xR Modified Std Star-4 Dormant Active Dormant DormantShift-xR Modified Std Star-4 Dormant Active Dormant Dormant — Shift-xRModified Std Star-4 Dormant Active Dormant Dormant Exit1-xR Modified StdStar-4 Dormant Active Dormant Dormant Pause-xR Modified Std Star-4Dormant Active Dormant Dormant — — — Select - Other Pause-xR Tech.Defined Other Dormant Dormant Dormant Active Exit2-xR Tech. DefinedOther Dormant Dormant Dormant Active Shift-xR Tech. Defined OtherDormant Dormant Dormant Active — Shift-xR Tech. Defined Other DormantDormant Dormant Active Exit1-xR Tech. Defined Other Dormant DormantDormant Active Pause-xR Tech. Defined Other Dormant Dormant DormantActive — — — Select-All Pause-xR Standard All Active Active ActiveActive Exit2-xR Standard All Active Active Active Active Update-xRStandard All Active Active Active Active

Table 1 lists various protocols that may be used with a SeriesEquivalent Scan. A protocol understood by the TAPCs of a selected branchis used to drive the state progression of a scan section. It is notnecessary that the TAPCs forming a deselected branch understand theprotocol used during this state progression. Scan operations areperformed on the selected branch while the other branches remaindormant. Branches that are not selected remain dormant and ignore theprotocol being used until they are selected. Once all branches areselected following the last scan section, the TAP controllers formingall branches move through the Update-xR and Capture-xR states in lockstep. This provides the function of a series scan.

In summary, a scan of the paths with a branch move the state of theTAPCs forming the branch to Pause-xR, sequentially selecting andscanning the scan paths of interest within each branch beginning andending the scans in the Pause-xR state. Once these scans are complete,the update/capture operation is performed simultaneously in all TAPCs ofall branches of interest The TAPC state may be moved from the Update-xRstate to either the Run-Test/Idle state or Select-DR state on to thePause-xR state where the sequential scans can again be performed. Thisprocess preserves the timing between the Update-xR and Capture-DR stateswhen portion of the operation that does not include the Shift-xR stateis performed using the Standard Protocol.

The Run-Test-Idle state may also be used to select branches. Thiscapability can be used to select a branch and park the state of one ormore of the TAPCs forming the branch. This may be sequentially done forall branches. Only those TAPCs within a branch that are not parked mayleave the Run-Test-Idle state. When all branches are selected and theTAPC state moved to the Pause-DR state via the Select-DR state. TheTAPCs whose state is parked in Run-Test-Idle state do not participate inthe scans.

A Selection Escape Sequence is used to initiate a selection sequence.This sequence can select all ADTAPCs within a branch while deselectionall ADTAPCs within other branches or select all ADTAPCs within allbranches. A deselection escape sequence deselects all ADTAPCs of allbranches. Although selection and deselection escapes can be associatedwith any ADTAPC state, they are expected to be used while in thePause-xR and Run-Test-Idle states. This process will be described inmore detail below.

DTS/TS Connectivity

The TAP.7 architecture supports both simple and complex systemconnectivity with a graduated set of capability. A system may deploy anymix of TAP.1s, TAP.7s, and potentially other legacy technologies asshown in FIG. 4, which is a block diagram of a target system with mixeduse of technologies and scan topologies.

Most systems will implement only one branch of the connectivity shown inthis figure. In most cases, the target system (TS) will only have alimited number of TAPs. Other architectures, represented by branches406, 407, can also be included as additional branches that are separatefrom those shown in FIG. 4 in a custom scan topology. These branches arecontrolled in manner similar to TAP.7 branches.

Technology Branches

FIG. 4 is the union of simpler types of connectivity called technologybranches. Each of the branches 402-407 shown in this figure may beoperated separately for debug purposes. They may also be operated in amanner that provides Series Scan Equivalency across the branchescontrolled with the TCK1 and TCK(C) signals. Proprietary technologiesare generally operated separately but may be operated with TAP.7controllers in as shown in Table 1. Other embodiments may have variouscombinations of branch operation.

Other embodiments may have various combinations of branch operation.Other embodiments may use different sets of commands, protocols, events,etc. The list of protocols in Table 1 is not intended to be limiting toembodiments of the invention in any manner.

The TAP.7 branches 403-405 have one or more TAP.7s connected in Series,Star-4, and Star-2 Scan Topologies. These branches contain logic toselect or deselect an ADTAPC, indicated generally at 410. This logicprovides for the selection and deselection of these branches withSelection and Deselection Escape Sequences. ADTAPC selection logic isoptional for T0-T2 TAP.7s and mandatory for T3 and above TAP.7s.Including this logic in T0-T2 TAP.7s supports their deployment insystems where T4(N) and T5(N) TAP.7s may be deployed.

The TAP.1 branch 402 includes a TAP.1 or a T0-T2 TAP.7 withouttechnology selection logic connected in series with other TAP.1 s orTAP.7s. It operates with the standard protocol and TAPs with the four1149.1 signals. This branch is selected using the TCK1 signal shown inthis figure as it has no built-in selection mechanism. T0-T2 TAP.7swithout selection must be included in a branch that is this type. TheADTAPC selection logic may be added to the current 1149.1 technology tomake it selectable using common connectivity.

Proprietary technologies 406, 407 may be connected in parallel with theTAP.7 branches provided: the technology has a dedicated clock and atleast one control/data input; the technology implements the technologyselection mechanisms and protocols defined by the 1149.7 standard; andthe clock pin of the technology is connected to the TCK(C) signal andthe control/data pin is connected to the TMS(C) signal.

As noted previously, a TAP.1 branch is selected by keeping its TCK orTMS signal separated from the signal of like name of branches and gatingone of the separate signals to deselect the branch. The gating of theTCK signal of this type of branch is used to select these types ofbranches. TAP.1 s and T0-T2 TAP.7s without the Technology SelectionLogic (TSL) are selected using this method. Any branch may be selectedusing this method if desired.

TAP.1 s and TAP.7s can be deployed in topology branches as shown inTable 2. Each of these topologies is considered a technology within thisdocument.

TABLE 2 Branch/technology deployment permissibility T0-T2 w/o w/ BranchProprietary TAP.1 TSL TSL T3 T4(W) T5(W) T4(N) T5(N) TAP.1 No Yes YesYes Yes Yes Yes No No Series TAP.7 No No No Yes Yes Yes Yes No No SeriesTAP.7 No No No No Yes Yes Yes No No Star-4 TAP.7 No No No No No Yes YesYes Yes Star-2 Proprietary Yes No No No No No No No NoChips, Components, and Boards

With the TAP.7 architecture, any part of the connectivity shown in FIG.4 may be deployed on a board, within a package, or within a chip. Thiscomprehends the packaging and integration trends since the inception ofthe 1149.1 Standard.

The IEEE 1149.1 test view allows only one TAPC per component. The 1149.7test view is a superset that allows multiple TAPCs per component. Withthe 1149.7 test view a component: is either a package containing one ormore chips, or a direct mount chip; provides access to one or more TAP.1or TAP.7 controllers through the same or separate pins; and providesaccess to proprietary TAPCs or other technologies through the same orseparate pins.

This superset blurs the boundary between board, component, and chip.This blurring allows operation across those boundaries as shown in FIG.5. When there is only one TAPC per component, the 1149.1 and 1149.7 testviews are described by boundary scan description language (BSDL). Whenthere is more than one TAPC per component the 1149.7 test view requireshierarchical scan description language (HSDL), plus BSDL for eachendpoint.

TAP.7 Deployment Scenarios

Series branches may be constructed from TAP.1s and four pin TAP.7s asshown in FIG. 6. This scan topology may share the TMS, TDI, and TDOconnectivity with another topology provided TCK(C) or TMS(C) signal isused to select/deselect this topology.

50BIn most cases, one or more TAP.7s is connected in one of the ScanTopologies shown in FIGS. 1-3. Note that the convention for naming DTSTDI/TDIC and DTS TDO/TDO signals in FIGS. 1-3X is: 1) The DTS TDI/TDICsignal sources chip TDI information; 2) The DTS TDO/TDOC signal is thedestination for chip TDO information.

The Star-2 Scan Topology illustrated in FIG. 3 is a subset of both theSeries and Star-4 Scan Topologies. This means that the Series and WideStar Scan Topologies may be operated as a Star-2 Scan Topology whenevery test access port sharing the connection is a T4 and above TAP.7.

Chip TAPC Hierarchy

A hierarchical view of TAPCs within a chip is needed to maintain IEEE1149.1 compliance and provide solutions to the compatibilityrequirements identified earlier. For a given chip, three or more levelsof TAPC hierarchy are accommodated as follows:

-   -   1^(st) level—a TAPC within the TAP.7 controller—the primary        interface to the DTS.    -   2^(nd) level—a TAPC at the chip-level (CLTAPC).    -   3^(rd) level —embedded TAPCs connected to the chip-level TAPC.    -   Other levels, if needed.        FIG. 10 is a block diagram illustrating bypass bits that are        provided to bypass the scan paths managed by the CLTAPC when it        is deselected. With a Series Scan Topology, the bypass bits        allow faster propagation of a scan data between the DTS's        TDI(C)and TDO(C) signals when the contents of the bypassed        component is not of interest.

While all levels of the TAPC hierarchy need not be present in all chips,the TAP.7 architecture accommodates them when they occur. The TAPChierarchy is shown in FIG. 7. Exemplary chip 700 includes TAPC 702 thatis implemented as a T0 with control events or a TSL for T1 and above.Chip level TAPC (CLTAPC) 704 operates under Adapter TAPC (ADTAPC) 700.Embedded TAPC(s) (EMTAPCs) 705 operate under CLTAPC 704. Additionallevels of EMTAPCs 706 may be embodied as needed. The EMTAPC(s) 705 andEMTAPC(s) 706 are hidden following a test reset.

A chip with IEEE 1149.7-compliant behavior always has a Chip-Level TAPC702. It may also include one or more Embedded TAPCs 704, all of whichare considered subordinate to the chip-level TAPC (CLTAPC). The CLTAPCis considered the parent of the Embedded TAPC(s). The addition of theEnhanced Protocol Unit (EPU) to a T1 or above TAP.7 controller adds theADTAPC but does not add an instruction or data registers in series orparallel with those associated with the CLTAPC and the EMTAPCs. TheADTAPC is considered the parent of the CLTAPC. The addition of theAdvanced Protocol Unit (APU) in a T4 or T5 TAP.7 does not add anadditional TAPC or level of TAP.7 TAPC hierarchy.

The ADTAPC 702 is connected to the CLTAPC 704. The CLTAPC may provideaccess to EMTAPCs. The EMTAPCs are hidden following a Test Reset topresent the test view of a component specified by the 1149.1 Standard.The “other TAPCs” portion of the hierarchy can have additional levels ofhierarchy. The TAPC hierarchy may vary dramatically by chip, with theTAPs accessed varying by application. In one or more embodiments of theinvention, the DTS dynamically manages the TAPC hierarchy to:accommodate a Star Scan Topology, minimize the length of the scan path,and avoid non-functional parts of the hierarchy.

Combined View of TAP Connectivity and TAPC Hierarchy

The combination of the system shown in FIG. 4 and the TAP.7 TAPhierarchy shown in FIG. 7 creates the system connectivity and TAPChierarchy shown in FIG. 8. The selection layers (labeled A-E) are shownthis figure. The entities actually selected and deselected are shown atthe bottom of this figure.

Selection Concepts

Additional selection concepts beyond those supported by the IEEE 1149.1standard are provided to access to the CLTAPCs and EMTAPCs shown in FIG.8. These concepts support: the use of the selection hierarchy, theparking of CLTAPC and EMTAPC states and resynchronization of the CLTAPCand EMTAPC to the state of their parent, and common signaling acrosstechnologies.

Hierarchical Selection and Deselection TAPCs

These concepts provide the DTS the means to interact with all or asubset of the technology connected to it. They provide a means to selectthe various levels of the hierarchy shown in FIG. 8. Lower levels of thehierarchy become usable when all nodes above it are selected and becomeunusable when any node above it is deselected. Selection and deselectionis provided at the following nodes in the hierarchy: specifictechnology, Series, Star-4, Star-2, or all TAP.7 Scan Topologies, anADTAPC within a TAP.7 Scan Topology (depending on the ADTAPC state), aCLTAPC connected to an ADTAPC, and EMTAPCs connected to a CLTAPC.

Determining the Scan Topology

In order for the Debug and Test System to select a particular scantopology, the TAP.7 controller's associated with a scan topology must beable to determine this association. The Debug and Test System can informa TAP.7 controller as to the scan topology in which it resides in simpleScan Topologies. This is not the case with complex scan topologies.

Since T0-T2 TAP.7s can only be used with a Series Scan Topology, theseTAP.7 controllers are presumed to be always operating in a Series ScanTopology. Since a T3 and above TAP.7 controller can be operated ineither a Series or a Star-4 Scan Topology, T4(W) and T5(W) TAP.7s can beoperated in Series, Star-4, and Star-2 Scan Topologies, and T4(N) andT5(N) TAP.7s can be operated in Star-2 Scan Topologies, a TAP.7controller's association one of these scan topologies must be determinedat run-time. This is accomplished using a process called Scan TopologyTraining

With T3 and above TAP.7s, a TAP.7 controller determines the scantopology in which it resides with Scan Topology Training as follows. TheDebug and Test System informs the TAP.7 controllers that Scan TopologyTraining is underway. It then stimulates the Scan Topology connected toit with TDI(C) and TDO(C) signal values and DR-Scans in a manner thatproduce differences in the TDI(C) and TDO(C) signal values and scan dataobserved by TAP.7 controllers in Series, Star-4, and Star-2 ScanTopologies. The TAP.7 controller records the TDI(C) and TDO(C) signalvalues along with scan data during Scan Topology Training in theTopology (TOPOL) Register. At the conclusion of the training, the TOPOLRegister value identifies the scan topology in which the TAP.7controller resides as the value of the TOPOL Register is are differentfor TAP.7 controllers deployed in Series, Star-4, and Star-2 ScanTopologies. Each T3 and above TAP.7 includes a TOPOL register, asindicated generally at 920 in FIG. 9.

Topology Register Function

The Topology Register values specify the topology as listed in Table 3.

TABLE 3 Topology Register Values TOPOL value Topology TDOC behavior 00Star-4 TDOC remains HI-Z 01 Series TDOC may be driven 10 Star-4 with TDOdrive TDOC may be driven allowed 11 Star-2 TDOC may be driven

As shown in Table 3, the Topology (TOPOL) Register value affects twooperating characteristics: it defines the TAP.7 topology that must bespecified during selection sequences for the TAP.7 to be placed Online;and it provides a means to HI-Z the TDO signal to prevent driveconflicts that could occur when the scan topology involves both Seriesand Star-4 Scan technology branches in certain cases (not describedherein).

Scan-Path Characteristics Used to Determine the Scan Topology

FIG. 9 is a block diagram illustrating system connectivity supported bythe TAP.7 architecture. Exemplary components indicated generally at 902represent the various components in the target system. Each componentincludes a scan path that is one or more bits in length. Pins havepull-ups to establish logic value when they not driven. The device 910does not have TDI(C) and TDO(C) pins. The internal inputs therefore area logic 1 for these pins. A debug and test system is connected to theTCK(C), TMS(C), TDI(C), and TDO(C) pins. It is capable of driving boththe TDI(C) and TDO(C) pins.

Referring again to FIG. 9, the following attributes of Series, Star-4,and Star-2 Scan Paths are used to determine the scan topology in which aTAP.7 controller is deployed. A Series Scan Topology provides scan-pathcontinuity via TDI(C) and TDO(C). Only one of the TDI(C) and TDO(C)signals may be connected to the DTS unless there is only one TAPconnected to the DTS. A Star-4 Scan Topology provides scan-pathcontinuity via TDI(C) and TDO(C). Both the TDI(C) and TDO(C) signals areconnected to the DTS. In a Star-2 Scan Topology the EPU's TDI signal andTDO inputs are fixed at a logic 1 value when these pins are either notimplemented or the TDI(C) and TDO(C) pins are used for alternatefunctions.

A two step process, scan connectivity and scan continuity testing, thatis orchestrated by the DTS exposes characteristics of a TAP.7controller's connectivity used to determine the Scan Topology.

The scan connectivity test records the TDIC and TDOC signal values whenboth of these signals are driven by the DTS. This test determineswhether a TAP.7 controller is deployed in a Star-4 Scan Topology. Alogic 0 created by the DTS at the TDIC and TDOC signals can only beobserved as such by TAP.7 controllers deployed in a Star-4 ScanTopology. TAP.7 controllers that are deployed in a Series or Star-2 ScanTopology observe either one or both of these signals as a logic 1. Whenthe connectivity test determines the TAP.7 controller is deployed in aStar-4 Scan Topology, this determination survives the connectivity testthat follows.

The connectivity test determines whether TAP.7 controllers that are notdetermined to be deployed in a Star-4 Scan Topology are deployed in aSeries or Star-2 Scan Topology. This determination is made based on thescan data values observed during an all zeroes DR-Scan whose length isgreater than the longest series scan path. A TAP.7 controller thatobserves logic 0 scan data is determined to be deployed in a Series ScanTopology while a TAP.7 controller that observes logic 1 scan data isdetermined to be deployed in a Star-2 Scan Topology. The connectivityand continuity tests are sufficient to determine the scan topology asshown in Table 4.

TABLE 4 Scan topology connectivity and continuity tests resultsContinuity test Scan data Connectivity test value observations alongTDIC and TDOC signal with no Star- 4 determination value observations byconnectivity test Scan Scan topology Data topology TOPOL TDIC TDOCdetermination observed determination Series 0b 1b No 0b Yes Series 1b 0bNo 0b Yes Series 1b 1b No 0b Yes Star-4 0b 0b Yes 0b — Star-2 1b 1b No1b YesScan Topology Training Command Sequence

Scan Topology Training utilizes the following sequence of commands toperform the connectivity and continuity tests: 1) CMD (STC2,APFC=Standard function), which configures the TDIC and TDOC pins of T4and above TAP.7s as the T3 TAP.7 pin functions unless inhibited by theChip-Level logic; 2) CMD (STC2, TOPOL=Star-4-HI-Z, unconditional), whichsets the Topology Register for all T3 and higher TAP.7s to Star-4-HI-Z;3) CMD (STMC, Test for Star-4 Scan Topology), which tests for a Star-4Scan Topology while the DTS drives both TDI(C) and TDO(C) to a logic 0during the Update-DR state of CP2 of the command; and 4) CMD (SCNB, Testfor Series Scan Topology), which tests for a Series Scan Topology with aCR Scan of all zeros whose length is longer than the longest possiblescan path.

The TOPOL Register records the results of connectivity and continuitytests performed by the STMC and SCNB Commands. The values of thisregister and their meaning are shown in Table 3. A Type-0-Type-3 Resetinitializes this register value to 00b indicating Star-4-HI-Z when thestartup option is Offline-at-Start-up-and to 01b indicating Series. Notethat the Test-Logic-Reset state (a Type-4 Reset) does not change thisregister value. Subsequent to this, Scan Topology Training or commandsmay alter this value.

Connectivity Test

The STMC Command is used to perform the connectivity test. This commanddetermines whether the scan topology is Star-4. The DTS drives theTDI(C) and TDO(C) signal values to a logic 0 value prior to theUpdate-DR state of Command Part 2 (CP2) of this command. The logic 0TDI(C) and TDO(C) values can be easily accomplished using the followingTAPC state machine state sequence to end CP2 of the STMC Command:

-   -   Exit1-DR>Pause-DR        (N)>Exit2-DR>Update-DR>Select-DR-Scan>Capture-DR>Exit1-DR>Pause-DR        (N)

The DTS may drive both TDI(C) and TDO(C) signals to a logic 0 beginningat a point within the first Pause-DR state and release the drive of theTDO(C) signal (or both signals) at a point within the second Pause-DRstate of this series of states. TAP.7 controllers deployed in a Star-4Scan Topology see both the TDI(C) and TDO(C) signals as a logic 0. TAP.7controllers that are deployed in either a Star-2 or Series Scan Topologysee at least one of these signals as a logic 1. The Update-DR state ofthis sequence samples the TDI(C) and TDO(C) values and sets the ScanTopology Register to 00b when TDI(C) and TDO(C) values are both a logic0 and 01b otherwise. A logic 0 value is sufficient to determine that theTAP.7 controller is deployed in a Star-4 Scan Topology.

Continuity Test

When the TOPOL Register value is 00b, the drive of TDO(C) is inhibited.This allows both the use of commands to deselect the CLTAPC when theADTAPC is placed online following being placed Online followingOffline-at-Start-up and the use of an SCNB Command to perform thecontinuity test without a drive conflict. With this TOPOL Registervalue, the TDO(C) drive is inhibited until the SCNB part of the test iscompleted. This prevents TDO(C) drive conflicts that would otherwise bepossible during the CR Scan of the SCNB Command. A Series Branch willdrive TDO while Star-4 and Star-2 Branches will not. Only one TAP.7controller may drive the DTS TDO(C) connection.

The SCNB Command determines whether the scan topology is Star-2 orSeries with TAP.7 controllers that have not already determined they aredeployed in a Star-4 Scan Topology. The CR Scan of this command uses allzeroes data with a length greater than or equal to the series scan-pathlength of the Series Scan Topology. The EPU Bypass Bit of a TAP.7controller in a Star-2 Scan Topology is a logic 1 at the end of this CRScan while the EPU Bypass Bit of a TAP.7 controller in a Series ScanTopology is a logic 0 at the end of this CR Scan. This differencedefines the scan topology when the Update-DR state of the CR Scanoccurs. The Update-DR state of the SCNB CR Scan also converts the 00bTOPOL Register value to 10b.

TABLE 5 Topology Tests/TOPOL register relationships TDIC or TDOC Scandata Resulting signal observed observed TOPOL TOPOL Test as a logic 1?as a == 1? Register Register value: Connectivity No x x 00b - Star-4HI-Z Yes x x 01b—Series Continuity x x 00b 10b - Star-4 x No 01b 01b -Series x Yes 01b 11b - Star-2

TABLE 6 TOPOL register initialization Type-0-Type-3 Reset?Offline-at-Start-up? Resulting TOPOL value: No x Yes Yes 00b—Star-4 HI-ZYes No 01b—Series

It should be noted that in the case where there are two scan topologies,the topology may be completely determined by a single test, depending onthe two scan topologies involved. Should there be more than the abovescan topologies involved, other technologies could also be detected withthese tests or by adding additional tests. Topologies could also be madeto learn about other Technologies sharing the DTS connection if desired.

FIG. 11 is a flow diagram illustrating topology discovery in a targetsystem having a plurality of components coupled with a scan path. A setof training commands are received 1102 that instruct each component togo into a training session. In this embodiment, the training commandsare: 1) CMD (STC2, APFC=Standard function), which configures the TDICand TDOC pins of T4 and above TAP.7s as the T3 TAP.7 pin functionsunless inhibited by the Chip-Level logic; 2) CMD (STC2,TOPOL=Star-4-HI-Z, unconditional), which sets the Topology Register forall T3 and higher TAP.7s to Star-4-HI-Z; 3) CMD (STMC, Test for Star-4Scan Topology), which tests for a Star-4 Scan Topology while the DTSdrives both TDI(C) and TDO(C) to a logic 0 during the Update-DR state ofCP2 of the command; and 4) CMD (SCNB, Test for Series Scan Topology),which tests for a Series Scan Topology with a CR Scan of all zeros whoselength is longer than the longest possible scan path.

Each component test access port observes 1104 logic levels that appearon the test interface pins, in this case the TDI and TDO pins. The pinsare driven by the DTS as described above.

Based on observing the pin behavior, each component test access portdetermines 1106 the connectivity of the test interface pins, in thiscase TDI and TDO, and the type of scan topology that surrounds thecomponent, as described in more detail with respect to Table 3.

The TOPOL Register value associates TAP.7 controller with a ScanTopology, and consequently its ADTAPC's selection characteristics. Oncethe Scan Topology training completes, the ADTAPC may be selected as partof the Scan Topology in which it resides. For example, if it determinesit is connected in a series topology, then the ADTAPC may be selectedwhen a Series Topology is selected or any TAP.7 scan topology isselected. If it determines that it is connected in a Star-4 topology,then the ADTAPC may be selected when a Star-4 Topology is selected orany TAP.7 scan topology is selected. If it determines that it isconnected in a Star-4 topology, then the ADTAPC may be selected when aStar-2 Topology is selected or any TAP.7 scan topology is selected.

Other Embodiments

While the invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various other embodiments of the invention will beapparent to persons skilled in the art upon reference to thisdescription.

Although the embodiments of the invention find particular application tosystems using Digital Signal Processors (DSPs), implemented, forexample, in an Application Specific Integrated Circuit (ASIC), otherembodiment may find application to other types of systems, which mayhave another type of processors. Another embodiment may also be a systemthat does not include a processor. An ASIC that embodies the inventionmay contain one or more megacells which each include custom designedfunctional circuits combined with pre-designed functional circuitsprovided by a design library, wherein some or all of the megacellsinclude a test access port.

An embodiment of the invention may be a substrate to which is attachedmultiple chips that have individual test access ports, commonly referredto multi-chip modules. An embodiment may include stacked die devicesthat have individual test access ports. Another embodiment may be asubstrate, such as a printed circuit board, to which is attachedmultiple chips that have individual test access ports.

As used herein, the terms “applied,” “connected,” and “connection” meanelectrically connected, including where additional elements may be inthe electrical connection path. “Associated” means a controllingrelationship, such as a memory resource that is controlled by anassociated port. The terms assert, assertion, de-assert, de-assertion,negate and negation are used to avoid confusion when dealing with amixture of active high and active low signals. Assert and assertion areused to indicate that a signal is rendered active, or logically true.De-assert, de-assertion, negate, and negation are used to indicate thata signal is rendered inactive, or logically false.

It is therefore contemplated that the appended claims will cover anysuch modifications of the embodiments as fall within the true scope andspirit of the invention.

What is claimed is:
 1. An integrated circuit comprising: (A) a firsttest clock lead, a second test clock lead, a test mode select lead, atest data in lead, and a test data out lead; (B) a first test accessport having a clock input connected to the first test clock lead andbeing free of the second test clock lead, having a mode input connectedto the test mode select lead, having a data input connected to the testdata in lead, and a data output connected to the test data out lead, thefirst test access port having class T0-T2 capabilities and being free ofany topology selection logic; and (C) a second test access port having aclock input connected to the second test clock lead and being free ofthe first test clock lead, having a mode input connected to the testmode select lead, having a data input connected to the test data inlead, and a data output connected to the test data out lead, the secondtest access port having class T0-T2 capabilities and including topologyselection logic.
 2. The integrated circuit of claim 1 in which the firsttest access port is connected in series with additional test accessports.
 3. The integrated circuit of claim 1 in which the second testaccess port is connected in any one of Series, Star-4, and Star-2 Scantopologies.